# Python Crash Course for C# Developers — Part 2: Data Structures

<p>on Variables: Why "y = x" Can Give You Two Very Different Results**</p> <p>Have you ever written this?</p> <p>x = 10<br /> y = x</p> <p>x = 20</p> <p>print(x)<br />

<p>So far every variable in these posts has held a single value. Real programs deal with collections: a list of customers, a record for each student. Python has four built-in

<p>Lists have built-in methods to modify them directly.</p> <h2> Adding items </h2> <div class="highlight js-code-highlight"> <pre class="highlight python"><code><span